It is common practice to expand cereal grains such as wheat, rice and popcorn by the application of heat in conventional ovens. Normally the receptacle containing the grains must be agitated during heating so that all of the grains are heated substantially uniformly without burning the popped or expanded kernels.
More recently, with the advent of microwave ovens, receptacles transparent to microwaves have been provided for popping grains, said receptacles having a lower region of restricted internal volume for retaining the unpopped kernels in a massed clump and an upper region of greater volume for collecting and containing the popped grains. A preferred configuration for such a receptacle is conical, and such a receptacle is disclosed in U.S. Pat. Nos. 4,158,760 and 4,156,806.
The receptacles of said patents require a specially designed supporting base or frame of microwave transparent material. A flat perforated lid is preferably provided for retaining popped kernels within the receptacle while allowing the escape of steam created by the heating of the kernels. Consequently, the capacity for storing popped grain is strictly limited by the downwardly restricted configuration of the conical wall.
Moreover, the receptacles of said patents are not designed or adapted to be used in combination with other receptacles for other purposes such as cooking and steaming foods.
Certain other corn popping receptacles of which I am aware are bulky and inefficient, do not nest well for storage, and require additional receptacles when used for other purposes.